The present invention relates to a method for injection molding thin resin substrates for optical disks such as CDs and DVDs, and a clamp pressure control method for same.
It is an object of the present invention to provide a clamping pressure control method for an injection-compression molding process, by which molding operation time is reduced without compromising the quality of molded articles, as well as the product quality of accurately molded articles is improved.
To achieve the above-described objects, the present invention provides a method for compression-molding an optical disk substrate, wherein molten resin is injected into a cavity between a stationary mold and a movable mold and molded into a desired shape by compressing the resin between the stationary mold and the movable mold.
When moving the movable mold to a predetermined position where a clamping force is generated between the stationary mold and the movable mold, positioning control of the movable mold is effected so as to move the movable mold at high speed. Upon detection of the movable mold having reached the predetermined position, the positioning control of the movable mold is switched to clamping force control, so that the clamping force generated between the stationary mold and the movable mold reaches a first target value, wherein the speed of the movable mold is regulated in accordance with a difference between a target clamp pressure value and the clamping force being applied. Upon detection of the clamping force having reached a second target value which is lower than the first target value, the clamping force control by speed feedback is switched back to the positioning control.
According to the clamping pressure control method of the invention, during the initial period of the injection-compression molding, high-speed position control is performed, which makes high-speed clamping control possible. Subsequently, clamping force control is performed by speed feedback based on a detected clamping pressure at a low speed, which enables fine regulation of clamp pressure in accordance with various pressure fluctuations in resin and thereby improves the molding accuracy. As a result, a reduction in operation time and stability in the product quality of an accurately molded article are both achieved.
While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings.